Apparatus for measuring dips of well strata



kiTM-Ljti umm E March ll, 1952 L. o. GOODWIN 2 588,717

APPARATUS FOR MEASURING UlfS OF WELL STRATA Filed May 25, 1946 3Sheets-Sheet l A70 /32 /JJ /J/f /35 INVENTOR.

March 11, `1952 L, o.- GOODWIN 2,588,717

APPARATUS FOR MEASURING DIPS OF'. WELL STRATA Filed May, 25, 1946 5Sheets-Sheet 3 85 o o V /7 4 IN VEN TOR.

Arron/VE l Patented Mar. 11, -1952 APPARATUS Foa MEASURING mrs F AWELLsrRA'rA Lloyd o. Godwin, Tulsa, Okla., assignor to Stanolind Oil and GasCompany, Tulsa, Okla., a corporation of Delaware Application May 25,1946, Serial No. 672,209

Claims.

1 This invention relates to the logging of `wells and is directedparticularly to the measurement `in a single well of the dip and strikeof strata penetrated'by it. Specifically, the invention is directed toapparatus for improving the accuracy of dip measurements by taking intoaccount ce-rtain of the' variables which either are not considered-orare not evaluated with suiiif cient accuracy in present methods of dipmeasurement.

Although a number of devices and methods have been proposed formeasuring the dip of strata in a well, the so-called spontaneouspotential dipmeter appears to be the only one which has' been developedand applied to any great extent. That .device employs three electrodesequally spaced around the wall-of a well to make three logs of thechanges in natural or spontaneous potential encountered in passingacross an interface from one stratum to another of different chemicalcomposition or porosity. The differences in depth-at which these changesaffect the various electrodes are carefully measured and used tocalculate th dip and strike of the interfaces.

For very large angles of dip such as those encountered around salt domesthe degree of precision to which the dips are measured by -thespontaneous-potential method is considered satisfactory. But when thedip angles are less For example, calculation shows that for dips ofaround 5 underestimating the actual diameter y by per cent introduces anerror of nearly per cent.v Overestimating by 20 per cent is onlyslightly .less serious, the error being around 16 per cent vto 17 percent.

Similarly,`.for holes of the usual diameter, the

percentage error in determining the difference in depth of an interfaceon opposite sides of a hole introduces approximately an equal percentageof error in the calculated dip. For example, in a lO-inch hole an errorin measur ing depth differences of, say, 0.2 inch Where the differencein depth of an interface is 1 inch, i. e., a 20 per cent reading error,vproduces a dip error of very nearly 20 per cent. for holes of largerdiameter yand for larger dips a 0.2-inch error in depth would be lessserious,

- but it is nevertheless 4a quantity always to be often-and widely fromthe size of the bit. Soft' I. formations may be eroded by the drillingfluid than 10, as is true cf.very many vstructures and formations inwhich highly` valuable deposits of oil, gas, and other minerals arefound, the indications given by this method are much less positive. Ithas been clearly shown over a period of several years of commercial-usethat, where the strata are nearly horizontal, the indications of dipgiven by this' dip-measuring instrument are at best only qualitative andnot quantitative. i

In the measurement of dips by this method at least two assumptionsapparently are made, which can contribute largely to the inaccuracy ofthe determinations. It is assumed, rs't, that the diameter of the vholeis known either from the size of the bit used or from independentmeasurements made with a caliper instrument; and, second, that thelongitudinal movement of the dipmeter instrument in the Ahole is exactlyequal to the movement of the upper end of the suspending `cab1e.

The magnitude of the possible errors arising from these assumptions inthe event they are unjustied will be appreciated when itis realandabraded by the drill pipe until the hole diameter is several times thebit diameter. Hard formations usually remain about the same as cut bythe bit; but, if they are unusually porous and the drilling fluid is ofdoubtful plastering ability, a mud iilter cake may-formen them thickenough'to reduce the diameter to a point where the pipe becomes stuck.vor. at the very least, difhculties are encountered in withdrawing orinserting the bit and drill collars. i

Furthermore, the changes in hole diameter may be very great and quiteabrupt-so much so that hole-diameter logs may often be correlated fromone hole to another by marker beds which are notably harder or softerthan the adjoining strata.

It is because of the abruptness and frequency` of these diameter changesthat caliper measurements of them are only of limited utility for takingthem into account for dip calculaf v Because of the differing stretch ofdrill ameter or an independent determination of it ized that thepercentager error in dip is roughly equal to the percentage error in thediameter.

by caliper logging is in many cases a source` of error.

As for the determination of depths and depth Of course,

vin 0.1- inch, or even less if possible;

ing cable Considering all these sources of friction and tions.

differences, if it is desired to know the depth of the instrument onlyto within several inches or a foot or so, the assumption that the inlstrument movement is lthe same as the movement of the upper end of thecable is probably permissible. `But for very accurate calculation ofdips, particularly when they are small, and the hole diameter is alsosmall, it is important to know the position of the instrument to withlHowever, the friction of the suspending cable against the walls of thehole, the friction of the instrumentcentering guides,'the pressure ofthe measuring electrodes, and the irregularities of the walls themselvesall contribute to make the instrument movement erratic, and jerkydespite the application of a uniform pull at the upper end of the cable.

Because of the -length of the cables employed it is essential to'consider their elasticity in relation to the unavoidable frictionalforces present and the fact that the instrument is moved rather slowly.Thus, static friction tends Vto hold the instrument fixed until thecable elongates instrument loose. Then follows an upward cable at thetop of the well.

movement against the lesser retarding force it is only made worse byfurther slowing, downv the movement of the upper end of the suspendinattempts to increase accuracy.

their variability, it seems clear that the measurement of instrumentposition to the desired precision by measuring the cable movement is theexception rather than the rule.

It is, accordingly, a primary object of my invention to provide forlogging the dip of well vstrata apparatus which is accurate for both'large and small angles of dip. Another object is to provide a method andapparatus of this type for accurately evaluating variables contributingto the uncertainty of dip determinalogging'method and apparatus by whichvaria- A vfurther object is to provide a dip-A spaced equally aroundinstrument I5.

tions in the diameter of the well bore are accurately measured for thepurpose of taking them into account in the calculation of dip. Anotherand more specific object is to provide adip-logging method and apparatuscapable of taking advantage of the erosion of soft formations to a holeof largediameter, the interfaces between formations in such holes beingdetected with the same accuracy as they are for -smaller diameter holes.Still a further object `is to provide a dip-logging method and apparatusin which the longitudinal movement of the instrument itself along thewell is ac- YThe principles and operation of my invention will be moreeasily understood by reference to the accompanying drawings illustratingcertain embodiments ofv the invention, and forming a part of lthisapplication. AIn these drawings, in which the same referencenumeral indifferent figures indicates the same or a corresponding part: y

in elevation an'embodiment of the invention suspended therein, togetherwith surface recoming and controlling equipment;

Figure 2 is a cross section of the lower end of a dipmeter deviceembodying the invention;

Figure 3 is a cross` s ectio'n of an anchor devicefor establishing "areference position in a well; l

Figure 4 is a cross section of a formationcharacte'r-measuringelectrode;

Figure 5 is a cross section of an alternative character-measuringdevice; and

Figure 6 is a cross section of a preferred ,type o'f character-measuringdevice.

Referringnow to Figure 1, intersected by a well II)v are a plurality ofstrata, such asstrata I I, I2,'and I3, of which the directions andangles are to 4be determined. Supported from the earths surface by acable I4, -which preferably contains a number of insulated conductors,is

a dipmeter instrument I5 hed in t-he center of well I0 by flexiblecentralizers I6. Projecting from instrument I5 and held by extendablelarms against the wall of well I0 are a pluralityI of formation-characterdetectors I1, Ila, etc., These are preferablyl at least three in numberspaced apart around the wall well I0. Connected by. a wire I8 todipmeter instrument I5 is an anchor device I9 having onextendable armsshoes 20and 2 I with sharp cleats for digging into the wall of well II]and holding firmlyl fixed anchorv I9 and the lower end of wire I8.v

The dipmeter instrument I5v is shown inI more detail in Figure 2, whereit will be seen that the detector I'I, for example, is carried at thepivot point of the pair of arms 30 and 3l, the other ends of which areattached to crossheads 32 and 33 within the body of instrument I5. Racks34 and 35, engaged by the gear 36 rotatable about.

shaft 2'8 which is fixed to the case of instrument v I5, are attached toand so control the vertical" movement of crossheads 32 and 33 that theymove together or apart in unison, producing a; movement of detector I1perpendicular with re-y spect to instrument I5. A tension spring 3lpulls crossheads 32 and 33 together, thus urging detectors I1, Ila',etc., outwardly into contact Withthe wall of well I0. Preferably theconstants of spring 31 are so chosen or adjusted as to maintain thepressure of detector I7 against the wall of well Ill fairly uniform overmost of the well diameters for which the instrument.

is designed to Work. This canbe done to a sufficient approximation by sochoosing spring 31 that the increase in lateral thrust applied todetector I1 as the crossheads move together Figure 1 is a cross sectionofa well showing tends to be compensated by the decrease in springtension.

An important feature of ythis instrument is the fact that the detectorsmove perpendicularly with respect to the instrument axis. If this werenot so, there would be a vertical component to their movement infollowing irregularities in the well walls which would make the exactdepth of the detectors depend on the well diameter.4 It should also benoted that by using suiiiciently long arms Aand 3l a very great range ofwell diameters can be logged. Thus, if a soft formation is considerablyeroded so that the hole diameter is large, the detectors are still ableto maintain contact with the hole wall and thus can locate interfaces asaccurately as for normal' diameters.

As the detectorsl1, I1a, etc., spaced at the same level around well I0move perpendcularly to and from the bodyof-instrument I5 in response tovariations in the well diameter, this Inove-l ment is indicated bychanges in an electrical circuit. One 0f a number of means foraccomplishing this is to mount an insulated contactor 40 on the end ofone of the racks such as rack 35, to which the radial movement of thedetectors is resistance wire 4I, one end of which may be grounded, as bythe lead 42,v By applying a voltage to contactor 4U through theinsulated lead` 43 extending to an indicator, the position of rack 35,and hence the diameter of the well, can be determined by the yportion ofresistance '4I included in the circuit.

As the equipment is ordinarily run into a well with the arms retractedbut releasable at the 'will of the operator, a notch 44 cut in the rackbar 34 is adapted to be engaged by a key 45. For releasing the mechanismwhen the desired -depth has been reached, a solenoid coil 48 energizedby electric current supplied from the surface v through an insulatedlead 49 pulls downward a.l v

plunger 50 actuating a lever 5I and withdrawing key 45 from notch 44.

Also within the upper portion of instrument I5 are means (not shown) fordetermining the inclination of the well bore and ythe directionalorientation of the detectors I1. Any of a number of commerciallyavailable devices are suitable for this use, it being preferable thatthe making of a direction and inclinationrecord b e con-l trollable fromthesurface, as by supplying a control current over an insulatedconductor to ini-l tiate or actuate the recording mechanism. One suchdevice is shown and its use in logging to determine the dip of wellformations is described in detail in U. S. ,Patent 2,427,950 to H.`G.Doll.I

The lower end of instrument I5 is devoted to means for indicating itsvertical movement in a well being logged. For this purpose the wire,I8is brought into the bottom compartment of inimparted, which contactorengages an elongated l end of reel 54 may have notches or gear `teethadapted to be engaged and held stationary by the tip of theferromagnetic core 60 of the solenoid 6I. By application of current tosolenoid 6| over the insulated lead 62 connecting it to the V l surface,the tipof core 68 may be withdrawn from and held out of contact withilange 59 so that the reel 54 can turn. Wire I8 is maintained taut atall times by suitable friction-brake means,

such as the brakeY 63 which is pressed against the reel iiange 64 by aspring 65.

n win be seen than with anchor le' fixed in place in the well thusfixing one end of wire I8,`

wheel 5I, so that from wheel 5|.-may be derived exact information of thelocation and motion of instrument I5 at any moment. An electricalindication of thisvrotation of measuring wheel 5I may be transmittedtothe surfaceor recorded l in a number of wa-ys. One meansprefeired for.its simplicity, is to provide vwheel 5I with a commutator 10consisting-cfa number of segments strument I5 through a packing gland50, passes over a measuring wheel 5I', with which it may be held incontact by'suitablerollers 52 and 53, and is wound on reel54. 'I heinsulated conductor, of which there is at least one in wire I8, isbrought out to a slip ring 55 contacted by an insulated brush 56connected to an insulated lead 51 extending to the earthssurface. Thereis thus provided a continuous insulated electrical circuit extendingfrom the surface to the anchor I9 by alternately of insulating andconducting material. A brush 1I, in contact with commutator 10 andconnected by an insulated lead 12 extending to the surface, produces anon-off signal when suitably supplied with voltage. There is thusprovided, simultaneously with the making of the threeformation-character'logs and the diameter' measurement, a directindication of the progress of the instrument through the well entirelyindependent of the motion of cable I4.

An embodiment of the conrollable anchor I9 is shown in more detail inFigure 3. Similarly to the mounting of detector I1 the cleated shoes A20 and 2I are mounted at the pivot points of the'V pairs ofaims 80, 8|and 82, 83, respectively. The

- urges arms 29 and 2I outwardly into firm contact with the well wallswhen anchor I9 is to be set.

4 AnchorA I9 vis run into a well with the arms retracted but releasable,and for the latter purpose a pin 88 engages a notch 89 in tube 86 whenthe tube` is ,in its uppermost position. `Pin B8 is withdrawn from notch89 by a lever 90 actuated -by the plunger 9| of a solenoid 92 whenvoltage is applied thereto by the operator over the wire-V I8, which hasan insulated conductor 93.

vFor retracting the shoes 20 andl 2| at the end of a survey, thelowcrend of ,tension spring 81.'

is attached to a notched plug 94 held in` its socket at the bottom endofv anchor I9 by n pin 95 which,- like pin B8, is withdrawn `fromholding 4plug 94 by a lever 96 actuated by the core 91 of a solenoid 99.Upon thus releasing the tension of spring 81, a smaller spring 99attached to the arms 8l and 83 is able to retract shoes 2l'I and 2I.Current to energize solenoid 98 may also'be supplied over the conductor93 of wire I8, the two solenoids 92 and 98 preferably being responsiverespectively to a low and a higher voltage. Application of a low voltageto wire I8 then opthe earths surface.

ascend? y duce a response. Thus, as shown by Figure 4,

the detector I1 may be a shoe of insulating material |I in .which is seta metallic electrode |02 connected by the insulated lea-d |03 to asuitable recorder at the surface. This will detect the spontaneouspotentials encountered along the wall of the well, which generallychange abruptly at the interfaces between strata.

Another device capable of very accurately loeating interfaces betweenstrata is shown in Figure 5. Set or moulded in the shoe |0| ofinsulating material are three small metal electrodes |04, |05, |06, eachof which is connected by a separate insulated lead inthe cable I4 toWhen current is passed between the center electrode I 05 anda distantpoint such as a grounded electrode at the earths surface, the potentialdifference between electrodes' |04 and |06 remains at zero exceptwhenthe electrode configuration crosses an interface between two strata. Thepotential difference then varies sharply, as disclosed in U. S.l Patent2,206,892, so that the interface can be very accurately located. As itis the difference in electrical resistivity of two strata rather thanlpo-v rosity or chemical composition which produces the response, theinterfaces located by this detector are often different from thosepicked up by the spontaneous-potential method.

This elect-rode `configuration -is particularly adaptable to locatingformation interfaces in wells which have been drilled using an oil-basebrations is translated into electrical current variations which can betransmitted over the insulated conductor |03 in cable I4'for'recordingat the surface of the ground. v

Referring again to Figure l, the surface recording and controllingequipment is seen to include the chart I2| which is moved in accordancewith the approximate depth` of instrument I5 in drilling fluid, Bysharpening the three electrodes |04, |05, and |06 so that they cut anarrow groove through the non-conducting lter cake and make vminute areaof the formation at any one time, 'so

that in passing or scraping over different formations the stylus iscaused to vibrate in different ways characterizing the respectivestrata. Thus, on the shoe III are mounted a. pointed scraping blade ||2,preferablyreplaceable, for cutting a groove in the filtercakeanormallyforming the wall of the well, and the pointed stylus I I3 which followsalong this groove. Being mounted onthe free end of a leaf spring II4, ofwhich the other endcis xed to the shoe I II, stylus I I3 in scrapingalong the bottom of the groove is free to vibrate relatively tothe shoelll'which slides smoothly over the surface of the filter cake and to thescraper |I-2 which contacts' an appreciable area of the bottom of thegroove. By suitable means such as an electrical strain gauge I|5cemented to spring' I I4, 'its resultant flexing with these vithe wellby an appropriate driving connection |22 from th'e sheave |23 over whichcable I4 passes. On chart I2 I' five traces are recorded by i therecorders |24, |25, |26, |21, and |28. The circuit of recorder |24,which includes the battery |29 in series with the lead 43 andcontactor40 of Figure 2, carries an electric current varying with the welldiameter, which is therefore indicatedv by the trace |30. The battery|3| maybe included in the circuit of commutator 10 and re` Yter-responsive detectors I1, Ila, etc. Of course, if the spontaneouspotential is ,being recorded,`

the batteries |36, |31, and |38 are omitted and the recorders |26, |21,and |28 are actuated :lccording to the magnitude of the potential at therespective pickup electrodes.

Several circuits are employed for controlling the subsurface operations.Thus, thelead 49 may be connected to the battery I4I and switch |42, thereturn circuit being completed throughA the metallic sheath of cable I4and the ground. When switch |42 is closed, voltage is applied tosolenoid 48 for releasing the arms carrying detectors I1 out intocontact with the walls of the well.

For controlling the operation of anchor I9, the vlead 51 i's brought outto the Switch |43 which, when thrown to :he left, applies the potentialof the battery |44 to solenoids 92 and 9B and when i thrown to the rightapplies to these coils the larger potential of battery |45. Battery' |44supplies suicient voltage to operate solenoid 92 for setting shoes 20and 2 I, but the larger voltage of battery |45 is needed for alsooperating solenoid 9B to bring about retraction of these shoes.

Actuation of solenoid 6I to unlock reel 54 for rotation is accomplishedby connecting lead 6 2 to the switch |46 and battery |41 so that closingthis switch applies voltage to the solenoid 6| as desired. In a similarway the inclination and orientation measuring equipment is actuated overa separate circuit including the switch |48 and potential source |49,switch |48 being closed momentarily whenever it is .desired to make ainclination.

lievedv apparent from the foregoing description, may be summarized asfollows: After lowering of the entire assembly to the bottom of thescction of the well to be logged. momentarily throwing switch |43 to theleft extends shoes 20 and 2| out against the wall of the well.

Then preferably the calipering and detector carrying arms are releasedby momentarily closing switch |42. Thereafter a record of theinclination of .the well and the orientation of the instrument should bemade by momentarily closing switch |48. Finally, when the logging is tobe started, switch |46 is closed, lifting plunger out of engagement withflange 59, and the ln- .strument I5 may then be moved slowly upward,

Each of the' The operation of my invention, -which 'is be# paying outwire I8 in accordance with its movement. At the top of the sectionlogged and as often as desired at intermediate positions, the movementmay be halted and switch |48 actuated to make records of the instrumentorientation and Y.

well inclination.

When the logging of a' section-of well is com pleted, switch |43 isthrown to the right to supply voltage for actuating plunger 91 `ofsolenoid 98 to release the tension of spring 81. Spring 99 then retractsshoes and 2 I. Thereafter, switch |46 may be opened, allowing plunger 60to lock reel 54 against further rotation, andv the entire instrument andanchor assembly may be removed from the well. For best resultsit isusually necessary to replace scraper blade II2 and stylus I I3 aftereach logging run. It is therefore no particular disadvantage to let thedetectors I1 slide along the well wall in extended position duringraising of the instrument to the surface of the ground.

Having thus described my invention in terms of the foregoing specificembodiments, numerous modifications thereof will undoubtedly occur' tothose skilled in'this art. The-scope of my invention should, therefore,not be considered as limited to the exact details of the method andapparatus described but isto be defined by the scope of the followingclaims.v

I claim:

l. Apparatus for logging wells comprising in combination a logginginstrument-adapted to be lowered into a well, a flexible support forsaid instrument, said support being slightly extensible with increasingtensiondue to the inherent elasticity of the materials forming it,.asecond flexible and Aextensible support depending from said instrument,an anchor fixed to the lower end of said second support, means forpaying out said second flexible support, permitting relative movementbetween said anchor and said lnstrument,

\ instrument is moved by said first cable away from said anchor, andmeans actuated by the movement of said second cable therethrough forindicating at the surface the length of said second cable between saidinstrument and saidl anchor during movement of said.y instrument throughthe well.

3. In an apparatus for' logging wells and adapted to be lowered intoawell on a cable which is slightly extensiblev with increasing tensiondue to the inherent elasticity ofthe materials forming it, thecombination which comprises a member adapted to carry a logging means,an anchor spaced from said member', wall- 10 l engaging means on saidanchor adapted to hold it fixed in a well bore, a flexible wireextending between said member andsaid anchor, means for `paying out saidwreas said member is moved by said cable away from said anchor, meansactuated rby the paying out of said wire for indi- 'eating at thesurface, during the moving of said -property characterizing theformations of said well carried at the outer extremity of each of:

said arms in Contact with the wall of said well, an anchor spaced fromsaid instrument, wall-engaging means on said anchor adapted to hold itfixed in a well bore, a exible wire connectingr said instrument and saidanchor and adapted to be payed .out upon movement of said instrumentaway from said anchor, means actuated by the movement of said wiretherethrough proportional to the movement of said instrument away fromsaid anchor, and means for vindicating simultaneously the responses ofeach said detector, the extension ofsaid arms, and the response of saidmovement-actuated means.v

5. Apparatusfor logging wells comprising an 'instrument adapted to bepassed through a well.

a plurality of arms pivoted to said instrument extendable outwardlytoward lthe wall of said well, a detector responsive to a propertycharacterizing the formations of said well carried at the outerextremity of each of said arms, an anchor spaced below said instrument,wall-engag ing means on said anchor adap"ed to hold it xed in a wellbore, a flexible wire connecting said i`nstrumentand said anchor, meansadapted to pay out said wire upon movement of said instrument REFERENCESCITED The following references are of record in the file of this patent;

UNITED sTATEs PATENTS *Number Name Date v1,339,955 Hardel May 11, 19202,150,070 Kregecz Mar. '7, 1939 2,313,176 Shelby Mar. 9,- 1943 2,340,987Robidoux Feo-8, 1944 2,398,562 Russell Apr. 16, 1946 2,408,012 WilliamsSept. 24, 1946 A2,483,770 Hildebrandt Oct. 4, 1949

